This invention relates generally to systems that generate electricity from the concentration of sunlight onto a photovoltaic semiconductor device, and more particularly to a low cost retrofitable multiple reflector system that can be modified on location to accommodate upgrades to its functional components.
Sunlight is a never ending source of energy that is available for conversion to electric power. The commercialization of solar electric power systems would avoid the disadvantages of other energy sources, such as air pollution, acid rain, the ozone problem, and nuclear waste. However, heretofore the cost of solar electric power has been too high to compete effectively with other types of electrical power generation, except in those relatively few instances where other types of commercially available power are not available, such as in remote locations.
Significant advancements for the efficient conversion of sunlight to electricity have been registered since the semiconductor revolution in the 1960's. As reported in Photovoltaic Insider's Report, March 1990, page 6, researchers at Stanford University, California, have increased the concentrated light solar cells' conversion efficiency to 28.5%. This is the best to-date reported for silicon. Varian Associates, California, has developed a multijunction solar cell with a 27.6% conversion efficiency, the highest "one sun" value reported to-date, as described in Semiconductor International, January 1990, page 16. These conversion efficiencies are adequate to allow solar electric power to meet the economic requirements necessary for commercialization, assuming that such highly efficient solar cells are reliable, can be manufactured at low cost, and can be integrated into reliable low cost systems.
Today, the terrestrial applications for solar electric products are restricted to those special uses where centralized network power is not practical, such as mountaintop microwave repeater stations, highway emergency telephones, and marine navigational aids. Prior art solar electric systems cannot compete economically with power generated by petroleum and coal for use in the central power networks due to the high cost of the solar electric power systems and their uncertain reliability.
In order for solar electric systems to become a valued contributor to central power networks on a cost effective basis, solar cell conversion efficiencies must remain high under production conditions, the associated solar electric system components must be low in cost, and all system components must be reliable enough to support the system's 30 year operating life. The commercialization of solar electric systems for central power network use will be determined by the system's cost per Kilowatt-hour of power generated over a 30 year period.
The most advanced prior art methods for concentrating sunlight onto photovoltaic products use a Fresnel lens or a curved (e.g. spherical, parabolic, or cylindrical) mirror. Each of these prior art design concepts have the limitation of requiring a tight alignment tolerance of a two axis solar tracker to keep the concentrated sunlight focused onto the photovoltaic component. The designed-in fixed size of the photovoltaic component is a further limitation of these prior art methods of light concentration. These prior art system designs have a further limitation in that they have a designed-in fixed concentration of sunlight which may be unsuitable to the requirements of the innovations in technology that are expected during the 30 year life of the solar power system. These prior art system designs do not lend themselves to low cost manufacturing concepts.
It seems likely that further technical advancements will be made in solar conversion photovoltaic products and light reflecting materials. Needed today is a solar electric power system designed to take advantage of the coming innovations in the performance and reliability of photovoltaic devices and light reflecting materials. Such a system design will provide assurance that the system will have a 30 year life because provisions for system upgrades to overcome component obsolescence will be a built-in feature of the design. The concentrator design of this invention carefully avoids those factors that impose limitations on the future use of this multiple reflector concentrator solar electric power system.